1. Field of the Invention
This invention relates in general to earth boring machines and in particular to an improved kelly seal for a hydraulic mast digger type earth boring machine.
2. Description of the Prior Art
Hydraulically powered boring machines known as "diggers" are presently used in the construction industries for drilling shallow holes, as for foundation piers. The digger is usually mounted on a truck and includes a hydraulic mast or cylinder twenty feet or more in length. A square bar known as a kelly is rotatably carried in the hydraulic cylinder and is rotatably driven by a hydraulic or gear driven rotary assembly through a drive bushing. The kelly has a head at its top which serves as a piston to move the kelly up and down in response to hydraulic fluid pressure in the hydraulic cylinder. A cutting tool, usually an auger, is secured to the bottom of the kelly for digging a hole.
The kelly head normally includes a set of bearings which are secured to the top of the kelly and mounted in a bearing sleeve. The bearing sleeve moves longitudinally in the hydraulic cylinder and the bearings allow the kelly to rotate with respect to the bearing sleeve. A cap, sometimes called a spindle, is secured to the top of the sleeve. The cap and bearing sleeve form a piston for movement in the cylinder in response to hydraulic fluid pressure.
The kelly is sealed at the bottom of the hydraulic cylinder by a packing assembly. The kelly seal at the bottom of the cylinder is subjected to high pressures and varying degrees of torque because the kelly may be rotating while it is being raised or lowered within the hydraulic cylinder. It is essential that the kelly seal at the lower end of the hydraulic cylinder be effective and long lasting in order to minimize fluid loss from within the hydraulic cylinder since the fluid serves to lubricate the kelly drive surfaces and provides the source of "crowd" or hoisting power for the kelly.
In one prior design, the packing assembly was rigidly affixed to a drive bushing located between the kelly and the rotary assembly of the device. As the drive bushing became worn with time, a certain amount of play developed between the drive bushing and kelly. The packing assembly surrounding the lower end of the kelly and rigidly affixed to the drive bushing became a point of torque transmission between the rotary assembly, drive bushing, and kelly. As a result, the packing was distorted due to the torque load and began to deteriorate causing a loss of hydraulic fluid.